U.S. patent number 8,165,228 [Application Number 11/688,708] was granted by the patent office on 2012-04-24 for non-coherent transmission method for uplink control signals using a constant amplitude zero-autocorrelation sequence.
This patent grant is currently assigned to Alcatel Lucent. Invention is credited to Jung A. Lee, Said Tatesh, Hai Zhou.
United States Patent |
8,165,228 |
Lee , et al. |
April 24, 2012 |
Non-coherent transmission method for uplink control signals using a
constant amplitude zero-autocorrelation sequence
Abstract
In one embodiment of the instant invention, a non-coherent
transmission method for uplink control signals is provided. The
transmission methodology uses a constant amplitude
zero-autocorrelation (CAZAC) sequence for relatively short control
signal lengths. The methodology includes creating a CAZAC sequence,
truncating the CAZAC sequence into a plurality of segments; and
transmitting each of the segments within a predetermined window of
time.
Inventors: |
Lee; Jung A. (Pittstown,
NJ), Tatesh; Said (Swindon, GB), Zhou; Hai
(Swindon, GB) |
Assignee: |
Alcatel Lucent (Paris,
FR)
|
Family
ID: |
39774649 |
Appl.
No.: |
11/688,708 |
Filed: |
March 20, 2007 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080232432 A1 |
Sep 25, 2008 |
|
Current U.S.
Class: |
375/260 |
Current CPC
Class: |
H04L
27/2607 (20130101); H04L 1/0073 (20130101); H04L
1/0028 (20130101); H04L 1/0026 (20130101); H04L
1/1607 (20130101) |
Current International
Class: |
H04K
1/10 (20060101); H04L 27/28 (20060101) |
Field of
Search: |
;375/260 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
NTT DoCoMo, Ericsson, Fujitsu, Mitsubishi Electric, Sharp, Toshiba
Corporation, CDM-based Multiplexing Method of Multiple ACK/NACK and
CQI for E-UTRA Uplink, Seoul, Korea, Oct. 9-13, 2006, pp. 1-6.
cited by examiner.
|
Primary Examiner: Payne; David C.
Assistant Examiner: Shah; Tanmay
Attorney, Agent or Firm: Williams, Morgan & Amerson,
PC
Claims
We claim:
1. A method for transmitting control information, comprising:
transmitting, from a mobile device, each of a plurality of segments
of a CAZAC sequence within a corresponding one of a plurality of
time-division multiplexed long blocks of a first slot of an ACK/NAK
channel, wherein a number of segments in the plurality of segments
is greater than or equal to the number of long blocks in the first
slot.
2. A method, as set forth in claim 1, further comprising combining
each of the plurality of segments with a cyclic prefix in the first
slot.
3. A method, as set forth in claim 1, comprising truncating the
CAZAC sequence to a length that is greater than or equal to the
number of long blocks in the first slot multiplied by a sequence
length associated with the long blocks.
4. A method, as set forth in claim 1, wherein transmitting each of
the segments further comprises mapping the plurality of segments of
the CAZAC sequence to long blocks of a slot structure including the
first slot.
5. A method, as set forth in claim 4, wherein mapping the plurality
of segments of the CAZAC sequence to the long blocks of the slot
structure further comprises mapping each of the segments of the
CAZAC sequence to a corresponding long block in the first slot.
6. A method, as set forth in claim 4, wherein mapping the plurality
of segments of the CAZAC sequence further comprises mapping at
least one of the plurality of segments to a reference signal block
in the first slot.
7. A method, as set forth in claim 1, wherein transmitting each of
the segments comprises transmitting each of the segments for
coherent combination of the long blocks at a receiver.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to telecommunications, and, more
particularly, to wireless communications.
2. Description of the Related Art
In the field of wireless telecommunications, such as cellular
telephony, a system typically includes a plurality of base stations
distributed within an area to be serviced by the system. Various
users within the area, fixed or mobile, may then access the system
and, thus, other interconnected telecommunications systems, via one
or more of the base stations. Typically, a mobile device (also
known as user equipment (UE)) maintains communications with the
system as the mobile device passes through an area by communicating
with one and then another base station. The mobile device may
communicate with the closest base station, the base station with
the strongest signal, the base station with a capacity sufficient
to accept communications, etc. Further, each base station may be in
communication with a large number of mobile devices.
In a cellular communications system, it is common to transmit a
reference signal along with each data signal. As those skilled in
the art will appreciate, the reference signal generally makes it
easier to properly detect the data signal, especially in non-ideal
environments. Accordingly, a large number of reference signals may
be needed to support a large number of mobile devices with active
communication links. In a reverse link (i.e., from the mobile
device to the base station), at least one reference signal is
needed for each mobile device. Thus, the number of mobile devices
that can be supported in the physical layer may be limited by the
number of reference signal sequences that can be generated.
SUMMARY OF THE INVENTION
In one aspect of the instant invention, a method is provided for
transmitting control information. The method comprises creating a
CAZAC sequence; truncating the CAZAC sequence into a plurality of
segments; and transmitting each of those segments within a
predetermined window of time.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be understood by reference to the following
description taken in conjunction with the accompanying drawings, in
which like reference numerals identify like elements, and in
which:
FIG. 1 is a stylistic block diagram of a communications system, in
accordance with one embodiment of the present invention;
FIG. 2 depicts a block diagram of one embodiment of a base station
and a mobile device used in the communications system of FIG.
1;
FIG. 3 is a stylistic representation of a time-frequency allocation
for an Acknowledge/No Acknowledge (ACK/NACK) channel;
FIGS. 4A and 4B depict alternative embodiments of a mapping of a
Zadoff-Chu sequence for an ACK/NACK transmission;
FIG. 5 depicts a stylized representation of a flow chart of one
embodiment of a control routine that may be implemented in the base
station of FIGS. 1 and 2;
FIG. 6 depicts a stylized representation of a flow chart of one
embodiment of a control routine that may be implemented in the
mobile devices of FIGS. 1 and 2;
FIGS. 7A and 7B illustrates alternative methodologies for
generating a sequence having a length 84;
FIG. 8 is a block diagram illustration of one embodiment of a
transmitter structure for the proposed signal structure;
FIG. 9 illustrates a block diagram of a mechanism for generating or
adding CP to truncated portions of a CAZAC sequence; and
FIG. 10 illustrates a block diagram of one exemplary embodiment of
a receiver structure.
While the invention is susceptible to various modifications and
alternative forms, specific embodiments thereof have been shown by
way of example in the drawings and are herein described in detail.
It should be understood, however, that the description herein of
specific embodiments is not intended to limit the invention to the
particular forms disclosed, but on the contrary, the intention is
to cover all modifications, equivalents, and alternatives falling
within the spirit and scope of the invention as defined by the
appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Illustrative embodiments of the invention are described below. In
the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
Turning now to the drawings, and specifically referring to FIG. 1,
a communications system 100 is illustrated, in accordance with one
embodiment of the present invention. For illustrative purposes, the
communications system 100 of FIG. 1 is a wireless telephone system
that employs any of a variety of standards commonly known to those
of ordinary skill in the art, although it should be understood that
the present invention may be applicable to other systems that
support data and/or voice communication. The communications system
100 allows one or more mobile devices 120 to communicate with a
data network 125, such as the Internet, and/or a public telephone
system (PSTN) 160 through one or more base stations 130 and
additional circuitry 138, such as a Radio Network Controller (RNC).
The mobile device 120 may take the form of any of a variety of
devices, including cellular phones, personal digital assistants
(PDAs), laptop computers, digital pagers, wireless cards, and any
other device capable of accessing the data network 125 and/or the
PSTN 160 through the base station 130.
Thus, those skilled in the art will appreciate that the
communications system 100 enables the mobile devices 120 to
communicate with the data network 125 and/or the PSTN 160. It
should be understood, however, that the configuration of the
communications system 100 of FIG. 1 is exemplary in nature, and
that fewer or additional components may be employed in other
embodiments of the communications system 100 without departing from
the spirit and scope of the instant invention.
Referring now to FIG. 2, a block diagram of one embodiment of a
functional structure associated with an exemplary base station 130
and mobile device 120 is shown. The base station 130 includes an
interface unit 200, a controller 210, an antenna 215 and a
plurality of channels: such as a shared channel 220, a data channel
230, and a control channel 240. The interface unit 200, in the
illustrated embodiment, controls the flow of information between
the base station 130 and upstream circuitry, such as the RNC 138
(shown in FIG. 1). The controller 210 generally operates to control
both the transmission and reception of data and control signals
over the antenna 215 and the plurality of channels 220, 230, 240
and to communicate at least portions of the received information to
the RNC 138 via the interface unit 200.
The mobile device 120 shares certain functional attributes with the
base station 130. For example, the mobile device 120 includes a
controller 250, an antenna 255 and a plurality of channels: such as
a shared channel 260, a data channel 270, and a control channel
280. The controller 250 generally operates to control both the
transmission and reception of data and control signals over the
antenna 255 and the plurality of channels 260, 270, 280.
Normally, the channels 260, 270, 280 in the mobile device 120
communicate with the corresponding channels 220, 230, 240 in the
base station 130 and may consist of both uplink and downlink
channels. Under the operation of the controllers 210, 250, the
channels 220, 260; 230, 270; 240, 280 are used to effect a
controlled scheduling of communications from the mobile device 120
to the base station 130.
In one embodiment of the instant invention, control signals, such
as ACK/NACK and CQI signals, are transmitted from the mobile
devices 120 to the base stations 130 using a code data multiplexing
(CDM) scheme. Considering differences in quality of signal (QoS)
(error rate, latency) requirements and the frequency of ACK/NAK and
CQI feedback, some embodiments of the instant invention may
successfully utilize a time data multiplexing (TDM) approach
between the two types of control signals for the mobile device 120.
In the illustrated embodiment of the instant invention, the ACK/NAK
channel structure is described and discussed; however, those of
ordinary skill in the art will appreciate that the instant
invention may find advantageous application in other channel
structures.
In one embodiment of the instant invention, a non-coherent
transmission method for uplink control signals is provided. The
transmission scheme uses constant amplitude zero-autocorrelation
(CAZAC) sequence for control signals. The CAZAC sequence occupies
an entire slot and is repeated over the two slots with frequency
hopping. At the receiver, non-coherent detection is employed.
Compared with existing solution, the invention provides a larger
number of sequences, and thereby supports a large number of users
with superior detection performance compared with existing
solutions.
Two alternative CDM approaches may be used for a non
data-associated control signal channel. Both of these alternatives
provide CDM using a constant amplitude zero-autocorrelation (CAZAC)
sequence. In particular, both approaches use a CAZAC sequence
specific to a particular mobile device 120 for transmitting ACK/NAK
information. This approach advantageously eliminates the need for
reference signal (RS) demodulation and is particularly suited for
transmitting small amounts of control information.
Turning now to FIG. 3, a typical time-frequency allocation for the
ACK/NAK channel is stylistically shown. The ACK/NAK transmission
occurs over a complete sub-frame, which is comprised of 2 slots in
time (slot 0 and slot 1 300, 302) and in a single resource block
(RB) 304, which in the illustrated embodiment is comprised of 12
sub carriers in frequency. Frequency hopping occurs at the slot
boundary.
FIGS. 4A and 4B respectively illustrate the two embodiments of the
ACK/NAK channel structures. In both schemes, the sequence is
repeated over two slots in a subframe. FIG. 4A illustrates a first
scheme in which a Length L=12 CAZAC sequence 400 is transmitted
within a long block (LB) repeated over N LBs, where N=6 in the
illustrated embodiment such that the Length-12 CAZAC is repeated
six times in the long blocks LB1-LB6 401-406. Those skilled in the
art will appreciate that each of the LBs 401-406 is preceded by a
cyclical prefix (CP) 408. Additionally, provision has been made for
an RS 410, but need not be utilized in the instant invention so as
to avoid the overhead associated therewith. Thus, in one embodiment
of the instant invention, no transmission occurs during the RS
410.
FIG. 4B illustrates a second scheme in which a CAZAC sequence 450
of length L=N.times.12 is mapped to multiple LBs 451-456 within the
slot. Additionally, since the RS 458 is not being used in the
second scheme, a portion of the CAZAC sequence 450 may be
transmitted during this period as well. A truncated Zadoff-Chu
sequence or a cyclic extension of the Zadoff-Chu sequence may be
considered to generate a length N.times.12 sequence, where N is the
number of LBs available, which in one embodiment includes LB1-LB6
and RS for a total of N=7. Those skilled in the art will appreciate
that a greater or lesser number of LBs may be employed, as desired.
For example, in some applications, it may be useful to use all
seven of the available LBs, while in other applications it may only
be necessary to use five of the available LBs. Proper programming
of the base stations 130 will allow them to retrieve the portions
of the CAZAC sequence from the appropriate LBs and then reassemble
the original Zadoff-Chu sequence.
As an example, a length L=13 Zadoff-Chu sequence may be used for
Scheme 1. For Scheme 2 with N=5/6/7, truncated Zadoff-Chu sequences
of lengths 61/73/87 may be used. Orthogonal sequences are generated
by cyclic shift of a root Zadoff-Chu sequence. The number of
orthogonal sequences for the two schemes are as follows:
Scheme 1: 12 orthogonal sequences are generated by cyclic shift by
one;
Scheme 2: 61/73/87 sequences are generated by cyclic shift by one
(where N=5/6/7).
Scheme 2 offers a substantially larger number of sequences, which
permits a larger number of mobile devices to be multiplexed in the
same time-frequency region.
Detection performance for the two ACK/NACK transmission schemes was
analyzed by link-level simulation. The simulation parameters are
shown in Table 1 below.
TABLE-US-00001 TABLE 1 Link-level simulation parameters. Parameter
Assumption Carrier frequency 2.5 GHz Transmission Bandwidth 10 MHz
Resource block size 12 sub-carriers Number of LBs for 5/6/7 LBs per
slot ACK/NAK (N) 2 slots with frequency hopping ACK/NAK structure
Scheme 1: Zadoff-Chu sequence (Length = 12) with N times
repetition. Scheme 2: Zadoff-Chu sequence (Length = N .times. 12).
N = 5/6/7 ACK/NAK detection Energy detection algorithm Scheme 1:
Coherent in same LB, non-coherent sum over LBs and slots. Scheme 2:
Coherent over LBs in a slot. Non- coherent over 2 slots. False
alarm probability 0.1% Channel model AWGN, GSM TU 3 km/hr Number of
transmit 1 antennas Number of receive 2 antennas
An energy detection algorithm with Neyman-Pearson criterion on
false alarm probability was used in the simulation. The number of
ACK/NAK LBs was 5/6/7. For Scheme 1, the detection metric was
computed by coherent accumulation in each LB, and by a non-coherent
sum over LBs and slots. For Scheme 2, the detection metric was
computed by coherent accumulation over all occupied LBs in a slot
and by non-coherent sum over two slots. In the simulation, Scheme 2
outperformed Scheme 1 by 3.7 dB for N=5 and by 4.2 dB for N=6 and
7, in AWGN channel.
Turning now to FIG. 5, a stylized representation of a flow chart of
one embodiment of a control routine that may be implemented in the
mobile devices of FIGS. 1 and 2 to implement Scheme 2 is shown. In
particular, the process begins at block 500 with the mobile device
120 preparing to send either an ACK or NAK control signal. At block
502, the control routine of the mobile device 120 truncates the
Zadoff-Chu sequence into a plurality of segments N, where N has
been previously established to represent the number of LBs that
will be occupied with each of the truncated Zadoff-Chu sequences.
Thereafter, at block 504, the sequence of CPs and LBs are
transmitted by the mobile device 120 to the base station 130.
FIG. 6 depicts a stylized representation of a flow chart of one
embodiment of a control routine that may be implemented in the base
stations 130 of FIGS. 1 and 2. The process begins at block 600 with
the base station 130 waiting to receive an ACK or NAK signal from
the mobile device 120. At block 602, the control routine receives
the transmission from the mobile device 120. Because N has been
previously established, the control routine of the base station 130
"knows" which of the LBs contain the truncated Zadoff-Chu
sequences, and thus, at block 604, the control routine retrieves
them from the appropriate segments. Thereafter, at block 606, the
control routine utilizes the truncated Zadoff-Chu sequences to
determine if an ACK or a NAK signal was transmitted by the mobile
device 120.
Those skilled in the art will appreciate that a reference signal
(RS) is not necessary for the based station 130 to properly
determine whether the mobile device 120 had transmitted an ACK or a
NAK signal. Accordingly, the instant invention does not suffer from
the overhead normally associated with the transmission of such
reference signals.
As discussed above, a basic CAZAC sequence of length P is
generated. In one exemplary embodiment of the instant invention, a
Zadoff-Chu sequence c.sub.p(n) of length P is generated using the
following equation:
.function..function..times..times..times..pi..times..times..times..functi-
on..times..times..times..times..function..times..times..times..pi..times..-
times..times..times..times..times..times. ##EQU00001## By selecting
different values for p, different root Zadoff-Chu sequence can be
generated. The number of sequences is (P-1) for a prime number P.
An orthogonal Zadoff-Chu sequence can be generated by a cyclic
shift operation of each of the root Zadoff-Chu sequences.
The number of samples that can be transmitted in a slot is
N.times.K, where N denotes the number of blocks (LB or RS blocks)
and K denotes the number of sub-carriers in a RB. To have the
maximum number of sequences, a prime length sequence is desirable.
For example, as shown in FIG. 7A, a sequence of length P=87 may be
generated according to the equation described above. Then, 3
samples 700 at the end can be truncated to produce a sequence of
length 84. Alternatively, as shown in FIG. 7B, a sequence of length
P=83 can be generated and cyclically extended to a length of 84.
This methodology could be specified in an industry standard or may
be configurable and known to the transmitter and the receiver. At
the receiver, the truncated or extended signal is detected by using
a correlator.
FIG. 8 is a block diagram illustration of one embodiment of a
transmitter structure 800 for the proposed signal structure. The
sequence of length (N.times.P) is broken into blocks of length P in
block 802 and converted from serial stream to parallel stream in
the S/P block 804 and transformed to frequency domain by a DFT 806
of length P. The frequency domain signal is mapped to a pre-defined
frequency region within the entire frequency band at block 808. For
example, this can be P sub-carriers at a pre-defined edge of the
system bandwidth. The unused sub-carriers are set to zeros. The
frequency domain signal is converted back to time-domain by IFFT
810 of size P. The output of the IFFT is parallel to serial
converted at block 812. The same procedure is applied for all N
blocks in a slot. Then, CP samples are added at block 816 before
transmission. The mechanism 900 for generating or adding CP is
conventional and is diagrammatically is shown in FIG. 9.
One exemplary embodiment of a receiver structure 1000 is shown in
FIG. 10. First, at block 1002 the signal portion corresponding to
the CP length is removed from the received signal in a slot of a
sub-frame. At block 1004, a signal of block length P is taken from
the received signal at a time, for N blocks. Thereafter, the signal
is converted to frequency-domain by an FFT 1006. A pre-defined
frequency resource is selected at block 1008. The selected signal
is multiplied by the reference signal at block 1010. The reference
signal is generated by taking the FFT 1012 of the basic signal of
length P, and by taking the complex conjugate of the FFT outputs at
the block 1014. The number of reference signals is (N.times.P), if
all (N.times.P) sequences are available in a cell. These signals
can be pre-computed and stored to reduce the amount of real-time
computation in the receiver. After the multiplication by the
reference signal, the signal is converted to time domain by an IDFT
1016. The energy is computed at blocks 1018, 1020 by taking the
magnitude square and combining the computed energy for all of the
blocks. At block 1022, the energy is then compared with a
threshold. If the energy within the search window exceeds the
threshold, the signal is detected.
Those skilled in the art will appreciate that the various system
layers, routines, or modules illustrated in the various embodiments
herein may be executable control units (such as the controllers
210, 250 (see FIG. 2)). The controllers 210, 250 may include a
microprocessor, a microcontroller, a digital signal processor, a
processor card (including one or more microprocessors or
controllers), or other control or computing devices. The storage
devices referred to in this discussion may include one or more
machine-readable storage media for storing data and instructions.
The storage media may include different forms of memory including
semiconductor memory devices such as dynamic or static random
access memories (DRAMs or SRAMs), erasable and programmable
read-only memories (EPROMs), electrically erasable and programmable
read-only memories (EEPROMs) and flash memories; magnetic disks
such as fixed, floppy, removable disks; other magnetic media
including tape; and optical media such as compact disks (CDs) or
digital video disks (DVDs). Instructions that make up the various
software layers, routines, or modules in the various systems may be
stored in respective storage devices. The instructions when
executed by the controllers 210, 250 cause the corresponding system
to perform programmed acts.
The particular embodiments disclosed above are illustrative only,
as the invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are
intended to the details of construction or design herein shown,
other than as described in the claims below. Consequently, the
method, system and portions thereof and of the described method and
system may be implemented in different locations, such as the
wireless unit, the base station, a base station controller and/or
mobile switching center. Moreover, processing circuitry required to
implement and use the described system may be implemented in
application specific integrated circuits, software-driven
processing circuitry, firmware, programmable logic devices,
hardware, discrete components or arrangements of the above
components as would be understood by one of ordinary skill in the
art with the benefit of this disclosure. It is therefore evident
that the particular embodiments disclosed above may be altered or
modified and all such variations are considered within the scope
and spirit of the invention. Accordingly, the protection sought
herein is as set forth in the claims below.
* * * * *